Multicomponent nanoparticle materials and process and apparatus therefor

ABSTRACT

Multicomponent nanoparticles materials and apparatuses and processes therefor are disclosed. In one aspect of the disclosure, separate particles generated from solution or suspension or by flame synthesis or flame spray pyrolysis, and the resultant particles are mixed in chamber prior to collection or deposition. In another aspect of the disclosure, nanoparticles are synthesized in stagnation or Bunsen flames and allowed to deposit by theirnophoresis on a moving substrate. These techniques are scalable allowing mass production of multicomponent nanoparticles materials and films. The foregoing techniques can be used to prepare composites and component devices comprising one ore more lithium based particles intimately mixed with carbon particles.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.12/633,629, filed on Dec. 8, 2009, which claims priority to provisionalapplication U.S. Ser. No. 61/193,582, filed on Dec. 8, 2008, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to multicomponent nanoparticle materialsand films and processes for forming the same.

BACKGROUND

Particle compositions have varied uses and are ubiquitous inapplications that exploit surface chemistry and physics. As the meanparticle size of the composition is reduced, the surface area increaseswith the square of the particle size. This results in a correspondingincrease in surface functionalities, e.g., reaction rate, due to theincrease in available surface area. Examples of systems that rely onhigh surface area for optimal performance include catalytic converters,dye sensitized solar cells, batteries, and fuel cells. Some of theseapplications use nanoparticle films that consist of more than one typeof nanoparticle. In such a system, various particles perform differentfunctions.

In certain types of fuel cells, for example, the simultaneous transportof protons and electrons requires some components of the film to serveas electron conductors, and others to serve as proton conductors (Haile,Chisoholm, Sasaki, Boysen, and Uda, “Solid acid proton conductors: fromlaboratory curiosities to fuel cell electrolytes”, Faraday Discussions134: 17-39, 2006). In another example, a film of at least two differentsizes of titania nanoparticles may be used to optimize the performanceof a dye sensitized solar cell (Vargas, “Aggregation and compositioneffects on absorption and scattering properties of dye sensitizedanatase TiO₂ particle clusters”, Journal of Quantitative Spectroscopy &Radiative Transfer 109: 1693-1704, 2008). In such a system, the largerparticles can scatter more of the incident light for more efficientcollection by the smaller particles, which dominate the surface area andthus photon-induced electron excitations.

A number of methods for depositing a particle film are known where theparticles are of the same composition. Tolmachoff et al. (Tolmachoff,Garcia, Phares, Campbell, and Wang, “Flame synthesis of nanophase TiO₂crystalline films”, Proceedings of the 5^(th) U.S. Combustion Meeting,Paper #H15, 2007) discloses a method for making thin films of titaniaparticles by repeatedly passing a substrate over a stagnation flame.Other methods of making single component nanoparticle films includescreen-printing or squeegeeing a nanoparticle paste (Llobet et al.,“Screen-printed nanoparticle tin oxide films for high-yield sensormicrosystems”, Sensors & Actuators B 96: 94-104, 2003), printing amicro- or nano-particle ink (US patent applications 20070169812 and20070169813), chemical vapor deposition (Zhu et al., “Growth ofhigh-density Si nanoparticles on Si₃N₄ and SiO₂ thin films by hot-wirechemical vapor deposition”, Journal of Applied Physics 92: 4695-4698,2002), or spray pyrolysis (Itoh, Abdullah, and Okuyama, “Directpreparation of nonagglomerated indium tin oxide nanoparticles usingvarious spray pyrolysis methods, Journal of Materials Research 19:1077-1086, 2004). These references, however, do not appear to disclosemethods of forming a film or materials containing a mixture ofcompositionally and/or functionally distinct nanoparticles.

Although compositionally and/or functionally distinct particles may bemixed in pastes or inks, the particles tend to agglomerate in suspensiondue to the high particle concentrations required for printing and stronginter-particle forces. Even if a surfactant were used, agglomerationwould continue after deposition as any surfactant would be lost duringthe drying and/or sintering process. This in turn limits the individualgrain size of a component in a multicomponent film to the micron scale,which is acceptable for forming films of particles that are notcompositionally different. Examples of methods that produce films madefrom a single composition particle are disclosed in patent applications20070169812 and 20070169813, in which an ink is formed from an organicsolvent and microflakes or nanoflakes produced by milling a solid havinga predetermined mixture of elements.

Patterned nanoparticle films can be made in colloidal solutions usingself-assembly techniques (see, for example, Sastry, Gole, and Sainkar,“Formation of patterned, heterocolloidal nanoparticle thin films”,Langmuir 16: 3553-3556, 2000). Here, the driving force is theelectrostatic interactions between like or unlike particles andmolecules. Although multiple particle types may be mixed, thesetechniques are generally very slow and are thus not suitable forcontinuous or large-scale fabrication of nanoparticle films.

Accordingly, a need exists for multicomponent materials, such ascomposites composed of distinct nanoparticles, and processes for theirmanufacture. There is also a need for such materials and processes tofeasibly mass produce certain types of fuel cells, solar cells,batteries and other devices that can utilize multicomponent nanoparticlematerials and films.

SUMMARY OF THE DISCLOSURE

Advantages of the present disclosure are multicomponent materials,processes and apparatuses for their manufacture.

These and other advantages are satisfied, at least in part, by acomposite, material or film comprising a mixture of a plurality of firstparticles and a plurality of second particles wherein the plurality offirst particles and the plurality of second particles have an averagesize of less than about 500 nm, e.g. less than about 200 nm.Advantageously, the plurality of first particles are compositionallydistinct from the plurality of second particles.

Embodiments of the disclosure include a plurality of first particlesintimately and randomly mixed with a plurality of second particles andwherein the plurality of first particles are composed of one or morecomponents selected from the group consisting of organic compounds,inorganic compounds, metals, electrocatalysts, metal oxides, lithiumactive compounds, metal hydrides, metal amines, solid acids, and saltsthereof and wherein the plurality of second particles arecompositionally distinct or have a significantly different average sizethan the plurality of first particles. The composite, material or filmcan also comprise a plurality of third, fourth, fifth, etc. particles.Other embodiments of the present disclosure include a compositecomprising one ore more lithium active compound particles, such aslithium-mixed metal oxides and phosphates, LiNiO₂, LiCoO₂, LiMn₂O₄,LiCoMnO₄, LiZnSb, LiFePO₄, and Li₂FePO₄F particles, with carbonparticles, wherein the lithium active compound particles have an averagesize of less than 100 nm and are intimately and randomly mixed with theplurality of carbon particles having an average size of less than 50 nm.

Other aspects of the present disclosure include processes of forming awell-mixed multicomponent material and film. The processes compriseforming a first aerosol; forming a second aerosol; and combining thefirst aerosol and second aerosol into a two-component aerosol to form acomposite material or film comprised of a plurality of first particlesfrom the first aerosol and a plurality of second particles from thesecond aerosol on a substrate. Advantageously the processes includeforming the plurality of first particles and the plurality of secondparticles with an average size of less than about 500 nm. The pluralityof first particles can be compositionally distinct from the plurality ofsecond particles, or the plurality of first particles can have anaverage size that is distinct from the average size of the plurality ofsecond particles. Alternatively, the plurality of first particles can becompositionally distinct from the plurality of second particles and canhave an average size that is distinct from the average size of theplurality of second particles. The aerosolized components can beindividually formed by spraying or atomizing a solution or suspension,or by flame synthesis or spray pyrolysis.

Other aspects of the present disclosure are apparatuses for providingmulticomponent materials and films by forming and combining distinctaerosols. For example, an apparatus can comprise a plurality of aerosolforming burners and/or atomizers that are in fluid communication with achamber for receiving and mixing a plurality of distinct aerosols.Embodiments include an apparatus comprising a first burner or atomizerfor forming a first aerosol; a second burner or atomizer forming asecond aerosol; a chamber in fluid communication with the first andsecond burner or atomizer for receiving and mixing the first and secondaerosols; and an exit port connected to the chamber for allowing theaerosols to escape the chamber, wherein the first burner or atomizer iscapable of either: (a) forming an aerosol that is compositionallydistinct from the aerosol formed from the second burner or atomizer or(b) forming an aerosol that has an average size that is distinct fromthe aerosol formed from the second burner or atomizer.

Additional advantages of the present invention will become readilyapparent to those skilled in this art from the following detaileddescription, wherein only the preferred embodiments of the invention areshown and described, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized, theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various respects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

Reference is made to the attached drawings, wherein elements having thesame reference numeral designations represent similar elementsthroughout and wherein:

FIG. 1 is a schematic illustration of an apparatus for generatingmulticomponent nanoparticle films, which includes multiple atomizers.

FIG. 2 is an electron micrograph image of a mixed porous nanoparticlefilm containing cesium dihydrogen phosphate, carbon, and platinumparticles where the cesium dihydrogen phosphate particles have anaverage size of about 50 nm, the carbon particles have an average sizeof about 20 nm, and the platinum particles have an average size of about20 nm.

FIG. 3 is schematic illustration of another apparatus for formingmulticomponent nanoparticle materials and films, which includes multipleatomizers and a particle forming burner.

FIG. 4 is a schematic illustration of another apparatus for generatingmulticomponent nanoparticle films, which includes a rotating plate overmultiple particle forming burners.

FIGS. 5A and 5B are electron micrograph images of a mixed nanoparticlefilm including titania and carbon particles on a glass substrate wherethe titania particles have an average size of about 15 nm and the carbonparticles have an average size of about 50 nm.

FIG. 6 is a schematic illustration of another apparatus for generatingmulticomponent nanoparticle films, which includes a rotating substrateover multiple particle forming burners.

FIG. 7 is a graph showing the size distribution of an aerosol mixturecontaining about 10 nm carbon particles formed from a premixed ethyleneflame and about 50 nm cesium dihydrogen phosphate particles formed bysolution atomization as determined by nano-SMPS analyzer (model 3936N25,available from TSI, Inc.).

FIG. 8 is a schematic illustration of another apparatus for generatingmulticomponent nanoparticle materials and films.

FIG. 9 is a top view illustrating a slot burner and atomizer of aparticle forming apparatus.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure is directed to materials, including materials inthe form of films, comprising a mixture of at least two sets ofparticles, e.g. a plurality of first particles and a plurality of secondparticles. The designation of first and second is solely for ease ofreference and does not limit the nature of the particles. Suchmulticomponent particle materials or films can include additionalparticles combined with the plurality of first and second particles,e.g. a plurality of third, fourth, fifth, etc. particles can be combinedwith the plurality of first and second particles.

In one aspect of the disclosure, the plurality of first particles andthe plurality of second particles have an average size at the nanometerlength scale. For purposes of the present disclosure, particles thathave an average size at the nanometer length scale are particles havingan average size of less than about 500 nm. Such particles are alsocalled nanoparticles herein. Preferably, the plurality of first andsecond particles have an average size of less than about 500 nm, e.g.less than about 200, 100, 80, 60, 40, 20, 10 nm and sizes there between.The average size of the particles can be determined by any conventionalmeans as, for example, by a particle sizer such as a scanning mobilityparticle sizer available from TSI, Inc. or equivalent instrument. Ifsuch instruments are not practical or available, other conventionalmeans for determining average size of the particles can be used such asby estimating a diameter for many particles in a material from anelectron micrograph image or equivalent image and taking an average ofthe estimated diameters.

Advantageously, the materials of the present disclosure can comprise amixture of compositionally different particles at the nanometer lengthscale, i.e., a composite of compositionally distinct nanoparticles.Compositionally distinct particles are those that have compositions thatvary by elemental composition and/or ratio of elements beyond the normalvariation expected for a given composition. Compositionally distinctparticles can serve different functions in the same material. In oneembodiment of the present disclosure, the material or film comprises amixture of a plurality of first particles and a plurality of secondparticles wherein the plurality of first particles and the plurality ofsecond particles have an average diameter of less than about 500 nm,e.g., less than about 200 nm, and wherein the plurality of firstparticles are compositionally distinct from the plurality of secondparticles.

The materials and processes for the preparation of such materials arebelieved advantageous compared to methods that involve mechanical mixing(such as ball milling a mixture) which usually produces grain sizes thatare on the micrometer scale. For example, it is believed that by millinga powder mixture consisting of nanometer-sized particles would result ina mixed powder that would still only have a grain size of roughly 1micrometer due to the tenacious van der Waals and electrostaticinteractions between nano- and micro-sized grains. Thus, even though theindividual particle sizes could be on the order of nanometers indiameter, the resulting mixture would feature single componentagglomerates on the order of micrometers in size. This precludes thepossibility of achieving random, dispersed or ordered patterns ofnano-sized grains in the mixture.

An advantage of the present disclosure is materials and films comprisingrandom and/or dispersed, compositionally distinct nano-sized particles.In one aspect of the present disclosure, the material or film includes aplurality of first particles that are intimately and randomly mixed witha plurality of second particles that are compositionally distinct fromthe first particles.

The multicomponent particle materials can be made from a number ofstarting particles. These include particles that can be formed in flames(such as carbon and metal oxides) or spray pyrolysis (such as metaloxides), as well as particles that can be formed from atomization anddrying of a solution or suspension (such as cesium dihydrogen phosphatein water and platinum nanoparticles in ethanol). The compositions of theparticles are limited to those which can be formed by an aerosol. Asused herein, an aerosol means a dispersion of solid and/or liquidparticles suspended in a gas. Aerosols can be formed from a mediumcomposed of a solid either dissolved or suspended in a solvent or liquidthat is sufficiently volatile to allow formation of particles in a flameor atomizer. Aerosols can also be formed by combustion of a hydrocarbonto produce solid carbon particles suspended in a gas such as theformation of carbon particles with a Bunsen burner.

Solvent or liquid mediums that can be used with atomizers include, forexample, one or more of water, alcohols and lower alcohols, e.g., aC₁-₁₂ alcohol, such as methanol, ethanol, propanol, isopropanol,butanol, furfuryl alcohol; polyhydridic alcohols, such as ethyleneglycol, butanediols, propanediols; ethers, such as linear or branchedlower ethers, dimethyl ether, ethyl ether, methyl ethyl ether,tetrahydrofuran; ketones and linear or branched lower ketones, such asacetone, methyl ethyl ketone; organic acids, such as formic acid, aceticacid, butyric acid, benzoic acid; esters, such as formats, acetates,propionates; hydrocarbons, such as linear or branched alkanes, such asbutanes, pentanes, hexanes, heptanes, octanes, linear or branchedalkenes, aromatic solvents or liquids; chlorinated solvents or liquids;etc. In an embodiment of the present disclosure, the solvent orsuspending liquid is an aqueous medium having one or more acids, e.g.HCl, or bases, e.g., ammonia, to adjust the pH of the medium and canalso include one or more surfactants and/or buffers.

The plurality of first, second, third, etc. particles can be composed ofone or more components selected from the group consisting of organiccompounds such as carbon, carbon nanotubes, and fullerenes; metals suchas aluminum, platinum, silver, gold, palladium, tin, titanium, indium,and zinc; metal oxides, such as alumina, tin oxides, titania, zincoxides, indium oxides, and zirconium oxide; semiconductors and oxidesand nitrides thereof such as silicon, gallium, cadmium, terrarium,silcon oxides, and silicon nitride; metal hydrides; metal amines; solidacids such as CsH₂PO₄, CsHSO₄, Cs₂(HSO₄)(H₂PO₄), (NH₄)₃H(SO₄)₂,CaNaHSiO₄, etc.; inorganic components, such as indium-tin-oxides,aluminum-doped zinc oxide, indium molybdenum oxide, antimony-tin-oxides,zinc doped with various other elements such as F, In, Ga, B, Si, Ge, Ti,Zr, Hf, Sc, Y, and salts of the forgoing, lithium active compoundsuseful for batteries, such as lithium-mixed metal oxides and phosphates,LiNiO₂, LiCoO₂, LiMn₂O₄, LiCoMnO₄, LiZnSb, LiFePO₄, and Li₂FePO₄F, etc.

The second set of particles can be composed of the one or more of theforegoing components but are either compositionally distinct or have anaverage size that is significantly different from the first plurality ofparticles. Preferably, the first and second plurality of particles havean average size that is less than about 500 nm and are intimately andrandomly dispersed throughout the multicomponent material.

The multicomponent materials can be used in a solid acid fuel cell, inwhich the anode includes a porous well-mixed nanoparticle film comprisedof solid acid particles, e.g., CsH₂PO₄, CsHSO₄, Cs₂(HSO₄)(H₂PO₄),(NH₄)₃H(SO₄)₂, CaNaHSiO₄, electron-conducting particles and electrocatalyst particles.

In an embodiment of the disclosure, a multicomponent particle filmincludes a plurality of solid acid particles, a plurality of conductingparticles, e.g., carbon, and a plurality of electrocatalyst particles,e.g., Pt, Ru, Rh, Pd, Cu, Ni, Ag, Au, Sn, etc. Such films can be used asproton conducting membranes for fuel cells as disclosed in, for example,U.S. Pat. Nos. 6,468,684; 7,250,232 and 7,255,962. As noted in thesepatents, many solid acids can be used for such films including compoundsof the general form: M_(a)H_(b) (XO_(t))_(c) or M_(a)H_(b)(XO_(t))_(c).nH₂O, where M is one or more of Li⁺, Bc⁺, Na⁺, Mg⁺, K⁺,Ca⁺, Rb⁺, Sr⁺, Cs⁺, Ba⁺, Tl⁺ and NH₄ ⁺ or Cu⁺; X is one or more of Si,P, S, As, Se, Te, Cr and Mn; and a, b, c, n and t are rational numbersand/or non-zero integers.

In optimizing a proton conducting membrane, transport of ions and gasesthrough the film should be considered and the porosity and themicrostructure of the film adjusted accordingly. For example, it isbelieved that optimizing a proton conducting membrane would include amembrane structure having high porosity and low tortuosity. It isbelieved such a structure can be made by including gas diffusionchannels embedded in the membrane by initially depositing fractal-likecarbon agglomerates to retain micro-sized open spaces in the membranefollowed by forming a multicomponent nanoparticle film in and among thecarbon composed of a mixture of solid acid particles, carbon particlesand electrocatalytic particles.

Multicomponent materials can also be used in batteries, such as lithiumor lithium-ion batteries in which the cathode comprises lithium activecompounds, such as lithium-mixed metal oxides and phosphates, LiNiO₂,LiCoO₂, LiMn₂O₄, LiCoMnO₄, LiZnSb, LiFePO₄, Li₂FePO₄F, etc. particles,together with carbon particles. In an embodiment of the presentdisclosure, a multicomponent nanoparticle composite comprises aplurality of lithium active compound particles, e.g. lithium ironphosphate particles, and a plurality of carbon particles.Advantageously, the lithium active compound and carbon particles areintimately and randomly dispersed throughout the composite. In an aspectof the present disclosure, the lithium active compound particles, e.g.lithium iron phosphate particles, have an average size that is less thanabout 200 nm, e.g., less than about 100, 50, 20 nm and sizes therebetween, and the carbon particles have an average size that is less thanabout 200 nm, e.g., less than about 100, 50, 20, 10 nm and sizes therebetween.

Lithium ion batteries are increasingly being made using lithium ironphosphate (LiFePO₄) as a cathode material. A primary advantage oflithium iron phosphate is that it is safer than other commonly usedmaterials (such as lithium cobaltate or lithium vanadate) because of aminimized risk of runaway heating and explosion. Upon discharge of thebattery, the iron (II) is oxidized to iron (III), the resulting freeelectron exits the battery through the load and returns to the anode,while the Li+ ion is transmitted to the anode through an electrolyte.Since the rate of discharge depends on the area of contact between theelectrolyte and the lithium iron phosphate surface, high performancebatteries require small grain sizes of lithium iron phosphate. An issuewith lithium iron phosphate, however, is that it exhibits poorelectrical conductivity, making it difficult for the free electron toexit the cathode, and thus limiting the discharge rate of the battery.

One way to overcome this deficiency is to intimately mix carbonparticles with the lithium iron phosphate grains in order to enhance theelectrical conductivity of the cathode. It is preferable that the mixinglength scale of the mixture be on the same scale as the grain size sothat electrons from each lithium iron phosphate grain may be efficientlyextracted and transmitted out of the cathode. In an embodiment of thepresent disclosure, a multicomponent nanoparticle composite compriseslithium iron phosphate particles and carbon particles which areintimately and randomly dispersed throughout the composite, wherein thelithium iron phosphate particles have an average size that is less thanabout 200 nm, e.g., less than about 100, 50, 20 nm and sizes therebetween and carbon particles have an average size that is less thanabout 200 nm, e.g., less than about 100, 50, 20, 10 nm and sizes therebetween. Additionally, the lithium iron phosphate particles can be dopedto enhance their performance such as by doping with one or more metalsincluding, for example, magnesium, aluminum, titanium, zirconium,niobium, and tungsten.

In an aspect of the present disclosure, multicomponent materials can beformed by combining a plurality of distinct aerosolized components inthe gas phase and collecting the mixture, such as by an electrostaticprecipitator, or depositing the mixture on to a substrate as a film orpowder. The aerosolized components can be individually formed byspraying or atomizing a solution or suspension, or by flame synthesis orspray pyrolysis.

In an embodiment of the present disclosure, a well-mixed, multicomponentnanoparticle material can be prepared by forming a first aerosol;forming a second aerosol; and combining the first aerosol and secondaerosol to form a material comprised of a plurality of first particlesfrom the first aerosol and a plurality of second particles from thesecond aerosol. The processes of the present disclosure are not limitedto forming materials with compositionally distinct particles but incertain embodiments the processes of the present disclosure can alsoform particles having distinct averages sizes. Hence, the plurality offirst particles can either: (a) be compositionally distinct from theplurality of second particles and/or (b) have an average size that isdistinct from the average size of the plurality of second particles. Inan embodiment of the present disclosure, the plurality of firstparticles: (a) are compositionally distinct from the plurality of secondparticles and (b) have substantially the same average size as theplurality of second particles. In another embodiment of the presentdisclosure, the plurality of first particles: (a) have substantially thesame composition as the plurality of second particles and (b) have anaverage size that is significantly different than the average size ofthe plurality of second particles, e.g., wherein the plurality of secondparticles have an average size that is no more than about two to fiftytimes of the average size of the plurality of first particles, e.g., 2,5, 10 or 50 times the average size of the plurality of first particles.In another embodiment of the present disclosure, the plurality of firstparticles: (a) are compositionally distinct from the plurality of secondparticles and (b) have an average size that is distinct from the averagesize of the plurality of second particles.

The first and/or second aerosols can be formed by atomizing a solution,atomizing a particle suspension, by flame synthesis and/or flame spraypyrolysis.

As used herein atomizing and atomization refer to the conversion of aliquid medium into a spray or mist (i.e. collection of drops).Atomization can occur by passing a liquid medium through a nozzle oraperture. The terms atomizing and atomization do not mean that the sprayor mist or the particles therefrom are reduced to atomic sizes.Atomization can also be described as “nebulize” or “nebulization”.Atomizing a liquid medium can be achieved by use of an atomizer.Atomizers are known and are commercially available, such as from TSI,Inc. of Shoreview Minn., USA.

Given the guidance of the present disclosure, one skilled in the art canselect the appropriate parameters to optimize the properties of theparticles, and their dispersion in a mixed particle film.

For example, an aerosol can be formed from a solution or suspension byatomizing the liquid into small droplets and then allowing the dropletsto dry into aerosol particles prior to and/or during mixing with theother aerosol particles formed in separate tubes. The atomization may beinitiated by injecting the liquid into a high velocity gas jet using asyringe pump or venturi aspiration. In forming a well-mixed nanoparticlefilm, it is preferable to control the vapor pressure of the liquid andthe number density of the droplets and resulting particles. For example,the liquid vapor pressure should be lower than its saturation vaporpressure so that the liquid does not recondense onto the particles oronto the film. This liquid vapor pressure can be kept low by limitingthe injection rate of the solution or suspension into the high velocityjet. Conversely, the saturation vapor pressure can be kept high bymaintaining the aerosol flow at a high temperature using a heatingelement such as heating tape, heating coils, and/or the heat generatedfrom a flame. The number density of the aerosol is preferably kept lowenough to minimize coagulation and agglomeration of the aerosol prior todeposition, which would increase the grain size of the particlescomprising the multicomponent film. The number density can be kept lowby quickly dispersing the aerosol in a clean sheath gas, or bymaintaining a low liquid injection rate.

Alternatively, or in combination, an aerosol can also be formed by flamesynthesis or flame spray pyrolysis with an appropriate burner. Creatingnanoparticles in a flame serves the dual purpose of keeping the mixedaerosol flow hot enough to prevent condensation if an atomizationmethodology is also used in parallel to the flame. Flame synthesistechniques involve the establishment of a premixed or diffusion flame,and passing one or more precursor compounds in a medium, if desired,into the flame where they are separated from their medium, if any,oxidized or undergo pyrolysis. The desired products of the oxidation orpyrolysis may nucleate and grow into the particles that ultimatelydeposit on the film. One example is the formation of metal oxideparticles by the oxidation of organometallic compounds. Flame synthesiscan also be used to form a plurality carbon particles by igniting a fuelwith an oxidant. This done by adding an excess of fuel or any otherhydrocarbon to the flame with respect to the stoichiometric amount giventhe oxygen flow rate into the flame. The excess carbon nucleates to formparticles commonly visualized as soot from a candle. The fuel cancontain a mixture comprising a hydrocarbon (e.g., one or more of analkane, such as propane, butane, an alkene, such as ethylene, an alkyne,such as acetylene, etc.) and optionally an inert gas (e.g., argon). Thefuel can also contain an oxidant, such as oxygen. Alternatively, theoxidant can be supplied separately to the fuel. When the fuel mixture isrich in hydrocarbon relative to oxidant, then all of the oxidant isconsumed thereby leaving an oxidant deficient environment, which can beuseful as a reducing environment for certain applications. Flame spraypyrolysis involves spraying solution droplets through an establishedflame in order to initiate droplet breakup, drying, and possibly thermaldecomposition in the high-temperature environment. The resulting aerosolcan then be collected such as by filtration, impaction, electrophoresis,thermophoresis or deposited as a film on a substrate that can be used ina device.

Passing the mixed aerosol through a porous substrate (having pore sizeof less than about 1 micron) results in a uniform well-mixed filmcomprised of the particles formed in each aerosol prior to mixing. Forparticles smaller than about 100 nm in diameter, the dominant mode ofcollection by the filter is believed to be diffusion, which results in auniform deposition pattern if the aerosol mass flow through the filteris uniform. This may be contrasted with particle collection byimpaction, such as by impinging an aerosol jet onto a flat substrate,which results in deposition patterns on the substrate that are sensitiveto the particle size and density. This mode of collection will notresult in a well-mixed film, as particles will separate based on theirinertia. However particle collection by impaction can be used to formwell-mixed multicomponent nanoparticle materials if the aerosolconcentration is sufficiently high to enable efficient agglomeration ofthe mixed aerosol particles, such that large agglomerates comprising amixture of the aerosol components are formed in the carrier gas andsubsequently impacted onto a substance.

In another aspect of the present disclosure, well-mixed multicomponentnanoparticle films can be formed onto a moving substrate by multipleflames oriented towards the substrate. Each time the substrate passesover a flame, a small mass (for example, less than a monolayer) iscollected on the substrate. Repeatedly passing the substrate overmultiple flames, each forming different types of nanoparticles, resultsin a well-mixed multicomponent film. The flames may be Bunsen flames orpremixed stagnation flames.

In an embodiment of the present disclosure, a multicomponent compositematerial can be prepared by combining an aerosol of lithium activecompound particles, e.g. lithium iron phosphate particles, or precursorsthereof with an aerosol of carbon particles to form the composite. Anaerosol of lithium active compounds can be formed, for example, byatomizing a precursor solution of the lithium active compound which canbe prepared by combining various lithium and metal compounds and saltsthereof in a medium. For example a lithium iron phosphate precursor canbe prepared from a number of precursors, including lithium precursorssuch as lithium acetate, lithium hydroxide, lithium nitrate, lithiumoxalate, lithium oxide, lithium phosphate, lithium dihydrogen phosphate,lithium carbonate, iron precursors such as iron sulfate, iron acetate,iron (II) oxalate, iron (III) citrate, iron (II) chloride, phosphateprecursors such as phosphoric acid, P₂O₅, etc.

For example, solid lithium iron phosphate may be formed in an aqueoussolution by combining lithium carbonate or lithium acetate withphosphoric acid, and iron (II) chloride or iron (II) oxalate. Underneutral stoichiometric conditions, LiFePO₄ precipitates as a greenishsolid having olivine crystal structure. However, the precipitation maybe suppressed by making the solution acidic. The pH of the solution canbe adjusted by adding such acids as HCl, nitric acid, sulfuric acid,acetic acid, etc. Such an acidic solution can be atomized and formedinto lithium iron phosphate by atomization, spray pyrolysis, etc. In oneaspect of the present disclosure, an aerosol of lithium iron phosphateis formed by atomizing an acidic solution of lithium iron phosphateprecursor by ultrasonic atomization, venture atomization, etc. Theaerosol can be subsequently carried to a flame produced by thecombustion of a hydrocarbon (e.g., one or more of an alkane, alkene andalkyne) and oxidant (e.g., oxygen), by a carrier gas, which may be aninert gas (e.g., nitrogen, argon, etc.) or fuel.

The flame can provide heat for micro-explosion of the aerosol dropletsand evaporation of the solvent to form nanoparticles of lithium ironphosphate. The flame can also be made rich with hydrocarbon fuel to formcarbon nanoparticles for combining with the resulting lithium ironphosphate nanoparticles which can then be co-deposited or collected. Anadvantage of using a flame rich with hydrocarbon fuel is that is willmaintain a reducing environment, so that the collected lithium ironphosphate does not oxidize to Fe (III), and so that any iron that hasoxidized to Fe(III) in the flame can be subsequently reduced back downto Fe(II).

A straight forward way to collect the aerosol particles is to pass theflow through a carbon filter, which itself can serve as a lithium ionbattery cathode. In this way, lithium active compound particles andcarbon nanoparticle production, mixing, and collection onto a batteryelectrode is accomplished in a single process. For example, a cathodeelectrode can be made by depositing a composite comprising a pluralityof lithium active compound particles intimately and randomly mixed witha plurality of carbon particles on to an appropriate substrate, e.g., asubstrate containing carbon and/or a fluorinated polymer such aspolyvinylidene fluoride (PVDF) and metal foil. Advantageously, theplurality of lithium active compound particles and carbon particles havean average size of less than 200 nm. In an embodiment of the presentdisclosure, the lithium active compound particles comprise lithium ironphosphate and have an average size of less than 100 nm and the pluralityof carbon particles have an average size of less than 50 nm.

In an aspect of the present disclosure, apparatuses are described thatcan form multicomponent materials, including materials in the form offilms, comprising a mixture of at least two sets of nanoparticles. Forexample, apparatuses can comprise a plurality of atomizers and/or aplurality of burners for forming compositionally distinct particlesand/or particles having distinct average sizes. The apparatuses of thepresent disclosure are not limited to forming materials withcompositionally distinct particles but in certain embodiments can alsoform particles having distinct averages sizes.

In one embodiment of the present disclosure, an apparatus for formingmulticomponent materials comprises: means for forming a first aerosol;means for forming a second aerosol; and means for combining the firstaerosol and second aerosol to form a plurality of first particles fromthe first aerosol and a plurality of second particles from the secondaerosol. The apparatus is configured so that the plurality of firstparticles and the plurality of second particles have an average size ofless than about 500 nm, e.g., less than about 200 nm, and/or theplurality of first particles are compositionally distinct from theplurality of second particles.

An apparatus for combining distinct aerosols can include a first burneror atomizer for forming a first aerosol; a second burner or atomizerforming a second aerosol; a chamber in fluid communication with thefirst and second burners or atomizers for receiving and mixing the firstand second aerosols; and an exit port connected to the chamber forallowing the aerosols to escape the chamber, wherein the first burner oratomizer is capable of either: (a) forming an aerosol that iscompositionally distinct from the aerosol formed from the second burneror atomizer or (b) forming an aerosol that has an average size that isdistinct from the aerosol formed from the second burner or atomizer. Thedesignation of first or second is for convenience and does not limit thenature of the particles or structure of the apparatus. Advantageously,the apparatuses can include chambers and/or exit ports in the form of aslot, and/or burners and/or atomizers having nozzles or apertures in theform of a slot, i.e., an elongated aperture.

FIG. 1 illustrates apparatus 100 that can be used to form multicomponentparticle materials and films. The conduits and lining of apparatus 100can be any material, such as those that do not substantially interferewith the formation of the particles including glass and stainless steel,etc. As shown in this illustration, aerosol film generator 100 can beused to form multicomponent films or powders on to a substrate 102, e.g.a carbon filter, by forming and combining several aerosolized componentswhich exit chamber 112 through exit port 126, which can be in the formof a slot. In the present illustration, first atomizer 104 forms firstaerosol 106 for forming a plurality of first particles and secondatomizer 108 forms second aerosol 110 for forming a plurality of secondparticles. The designation of first or second is for convenience anddoes not limit the nature of the particles or structure of theapparatus. Atomizers 104 and 108 can be any atomizers such ascommercially available atomizers or can be fabricated as a venturiatomizer that can be used to form aerosolized particles. Atomizers 104and 108 can have nozzles in the form of a slot.

First and second atomizers (104, 108) are in fluid communication withchamber 112. In this embodiment chamber 112 is a tube connecting firstatomizer 104 to second atomizer 108. However, Chamber 112 can be in theform of a slot. Chamber 112 connects the atomizers and allows mixing ofthe aerosols. As shown in FIG. 1, chamber 112 is in fluid connection toa heating element 114. In this embodiment, heating element 114 comprisesconduit 116 in fluid communication and connected to chamber 112 whichcarries a gas, e.g. an inert gas such as argon or nitrogen, which isheated by passing through conduit 116 which is heated by heating tape118 contacting the conduit. The heating element can be used to dry anyatomized liquid, i.e., the first and/or second aerosols, and/or tominimize or prevent recondensation of any liquid from the first and/orsecond aerosol. Preferably, chamber 112 and conduit 116 are constructedof stainless steel. Vents 120 and 122 can be used to control thepressure inside chamber 112 as, for example, when the pressure dropsacross a porous substrate with increased loading. In this embodimentvent 122 is connected to pump 124 for further control of the pressurewithin chamber 112 and/or the rate at which the aerosols leave exit port126.

FIG. 3 illustrates another apparatus that can be used in the formationof multicomponent particle materials and films. As shown in thisillustration, apparatus 300 can be used to form multicomponent films onto substrate 302 by forming and combining several aerosolizedcomponents. In the present illustration, first aerosol 304 is formedfrom first atomizer 306. Second atomizer 308 can be used to form secondaerosol 310. Atomizers 306 and 308 can be any atomizers such ascommercially available atomizers. First and second aerosols (304, 310)are mixed in mixing tub 312. Mixing conduit 312 is in fluidcommunication with the first and second aerosol. As shown in FIG. 3,third aerosol 314 can be formed from flame nozzle 316. In thisembodiment, flame nozzle 316 can form an aerosol of carbon nanoparticlesby igniting a mixture comprising a hydrocarbon (e.g., one or more of analkane, such as propane, butane, alkene, such as ethylene, alkyne, suchas acetylene, etc.) with and oxidant (e.g., air, oxygen) and optionallywith an inert gas (e.g., argon).

When fuel and carrier gas are rich in a hydrocarbon, the combustionproducts of the hydrocarbon includes carbon particles produced at flamewhich can intimately and randomly mix with aerosol. Further under suchconditions, the mixing conduit is substantially free of oxidant becauseany oxidant, e.g., oxygen, is consumed during the combustion of thefuel. When an aerosol from an atomizer is introduced to the mixingconduit under such conditions and is carried by a gas substantially freeof oxidants, e.g., such as by a nitrogen stream or even a hydrocarbonstream, the conduit comprises a reducing environment for the aerosol.

The heat from the combusted gases can be used to dry first and secondaerosols 304, 310. Particles from aerosols 304 and 310 can then becollected through exit port 320 as well mixed nanoparticles. In thisembodiment, the particles from the aerosols are collected on substrate302.

FIG. 4. Illustrates another apparatus for preparing multicomponentparticle materials. Apparatus 400 includes Bunsen burner 402 forgenerating an aerosol of carbon nanoparticles 404 that can be formed bycombusting hydrocarbons, which are collected on plate 406 rotated byspindle 408 attached to a motor (now shown for illustrative convenience)for rotating spindle 408 and plate 406. The apparatus further includesburner 410 for generating stagnation flame 412 which can produceadditional nanoparticles. By this apparatus, a plurality of firstparticles can be generated by Bunsen burner 402 and a plurality ofsecond particles can be generated by stagnation burner 410. Theseparticles are collected and mixed while being deposited on plate 406 andthe formed material can then be removed from the plate.

FIG. 6 is a schematic illustration of a burner set up using a pluralityof burners (shown in FIG. 6 as burners 602, 604, 606) that can be usedto form one or more multicomponent films on a substrate. Each burner canbe configured to form more than type of aerosol against substrate 608.In this example, burner 602 is configured as an aerodynamically shapedslot but any one or multiple burner configuration can be used. Forexample, a stagnation flame can be formed through a suitably shapedburner, such as an aerodynamic nozzle, tubular or slot burner. Eachburner is used to form a stagnation flame (not shown for illustrativeconvenience) which can be stabilized by substrate 608 which can bemovably positioned over each burner so as to form a continuously movingsubstrate. In this example, substrate 608 stabilizes the plurality ofstagnation flames and is in the form of a long sheet; however, othersubstrate forms can be used depending on the positioning of the burners,e.g., a disc can be used with multiple burners arranged in a circle. Asshown in FIG. 6, substrate 608 is moved over the burners by rotatingdrums 610. In FIG. 6, drum 610 is directly over a burner with thesubstrate there between. While it may be advantageous to have the drumsmore or less directly over the burners, as for example, to aid incooling the substrate, the drums need not be so positioned. Some or nodrums may be over the burners.

The arrangement in FIG. 6 provides several advantages. By using aplurality of burners, the substrate temperature can be maintained at alower temperature by moving the substrate against the multiple flames ata faster rate that it would need to pass against a single burner tomaintain the same rate of deposition of material on the substrate. Useof multiple burners also permits faster deposition of materials on thesubstrate. Moreover, by using a plurality of burners, each burner andstagnation flame can be individually configured to depositcompositionally distinct particles and/or particles having distinctaverage sizes on to the moving substrate. Each burner can beindividually configured to produce any stagnation flame and to produceeither the same or different particles on the moving substrate. Theformed particles can then be removed from the substrate and used as amulticomponent particle material or film.

FIG. 8 is a schematic illustration of another apparatus for formingmulticomponent materials. As shown in this illustration, apparatus 800includes conduit 802 for carrying fuel 804, e.g., a hydrocarbon and/or ahydrocarbon with an oxidant and/or with a carrier gas, through port 806which is in fluid communication with conduit 802. Fuel 804 is carriedalong conduit 802 to aperture 812 which contains a porous plug (whichcould alternatively be a screen mesh and to chamber 806 where it ismixed with carrier gas 808 which is introduced to chamber 806 throughport 810. In this embodiment, conduit 802 and aperture 812 are includedwithin chamber 806 and chamber 806 also contains flow straighteningelement 814, which can be made of a porous material such as compressedbrass. Flow straightening element 814 is used to distribute the flow ofcarrier gas 808 to chamber 806. Flow straightening element 814 can beflush with the top of conduit 802 or can be some distance below the topof conduit 802.

An ignition source (not shown for illustrative convenience) is used toignite fuel 804 at aperture 812 above flow straightening element 814 inchamber 806 to form flame 816. Carrier gas 808 can be air or anotheroxidant and can contain one or more inert gases, e.g., nitrogen, argon,etc. When fuel 804 contains sufficient oxidant for combustion, carriergas 808 can be composed substantially of one or more inert gases. Whenfuel 804 does not contain sufficient oxidant for combustion, carrier gas808 can contain an oxidant, e.g., oxygen.

As shown in FIG. 8, apparatus 800 further includes conduit 820 in fluidcommunication with atomizer 822 through port 824 for carrying an aerosol826 to chamber 806 and through exit port 830 as particles 832. In thisembodiment, conduit 820 is within conduit 802. As shown in thisembodiment, port 828 of conduit 820 is flush with aperture 812 but itcan be some distance above or below it.

By the configuration shown in this embodiment, aerosol 826 passesthrough flame 816 in to chamber 806. When aerosol 826 passes throughflame 816 it is subject to the heat and to the combustion productsproduced in the flame. When fuel 804 and carrier gas 808 are rich in ahydrocarbon, the combustion products of the hydrocarbon includes carbonparticles produced at flame 816 which can intimately and randomly mixwith aerosol 826. Further under such conditions, chamber 806 issubstantially free of oxidant because any oxidant, e.g., oxygen, isconsumed during the combustion of the fuel. When aerosol 826 isintroduced to chamber 806 under such conditions and is carried by a gassubstantially free of oxidants, e.g., such as by a nitrogen stream oreven a hydrocarbon stream, chamber 806 comprises a reducing environmentfor aerosol 826 because of the lack of oxygen and/or the availability ofcarbon which can react with oxidized components. The aerosol and anycarbon particles produced by combustion of fuel 804 are carried downchamber 806 by carrier gas 808 to exit port 830 where the particles canbe collected such as by filtration, impaction, electrophoresis,thermophoresis or deposited as a film on a substrate that can be used ina device. Further, aerosol 826 and particles formed therefrom can beheated by the combustion of fuel 804 and/or chamber 806 which can alsobe heated by the combustion of fuel 804 and/or an external heater notshown. Chamber 806 can be made of such a length so that aerosol 826 andparticles formed therefrom and production products from the flame have aparticular residence time in the environment of chamber 806 such as toanneal and/or reduce particles formed from aerosol 826. In oneembodiment, chamber 806 is at least one meter in length.

Apparatus 800 can be made of any materials that do not substantiallyinterfere with the operation of the apparatus or constituent parts. Forexample, conduit 820 can be made of glass or stainless steel, etc.;conduit 802 and porous plug in aperture 812 can be made of aluminum,brass, steel, etc.; chamber 806 and ports 806, 810, 824 can be made ofaluminum, steel, etc.

FIG. 9 is a top view of an apparatus for forming multicomponentmaterials. As shown in this illustration, apparatus 900 includes chamber902, burner 904 and conduit port 906 which are in the shape of a slot,i.e., an elongated aperture. When in operation, burner 904 can produce aflame that is in the shape of a slot which can then impinge a carriergas flowing through or around the slot flame. The slot flame can also beconfigured to impinge a substrate. In this embodiment, conduit port 906is contained within burner 904 but it can be located outside burner 904.Conduit port 906 can be used to introduce an aerosol to chamber 902. Anyof the forgoing illustrated apparatuses can have a chamber, burner,and/or atomizer in the shape of a slot. An advantage of a slot burnerand/or chamber is that particles produced therefrom and therein cancover and deposit on to a larger area to make thin films of well mixedparticles.

EXAMPLES

The following examples are intended to further illustrate certainpreferred embodiments of the invention and are not limiting in nature.Those skilled in the art will recognize, or be able to ascertain, usingno more than routine experimentation, numerous equivalents to thespecific substances and procedures described herein.

In an example of forming multicomponent nanoparticle films, solid acidfuel cell anodes were produced on carbon substrates, such as Toray paperavailable from Fuel Cell Scientific, LLC. Such anodes comprise mixednanoparticles films composed of solid acid nanoparticles, e.g., cesiumdihydrogen phosphate (CDP), conductive nanoparticles, e.g. carbonnanoparticles (C), and electrocatalyst nanoparticles e.g., platinumnanoparticles (Pt).

Using an apparatus as illustrated in FIG. 1, a range of films havingvarying C/CDP/Pt mass ratios, CDP particle size, and total mass wereformed. The features of these samples included: 1) films having wellmixed particles, and 2) films having tunable grain sizes that can befabricated with an average size of as small as about 10 nm and as largeas about 500 nm. A sample electron micrograph image of a multicomponentC/CDP/Pt particle film is shown in FIG. 2. Example parameters used inthe formation of such multicomponent films using an apparatus asillustrated in FIG. 1 are as follows. An aqueous CDP solution having aconcentration of about 0.5 mg/mL was prepared by reacting cesiumcarbonate (available from Alfa Aesar) and ortho phosphoric acid(available from Alfa Aesar). The aqueous CDP solution was atomized in afirst atomizer at a rate of about 0.4 mL/min. The resulting dropletswere further fragmented in the hot gas from the heating column having atemperature of about 250 degrees Celsius. The resulting dry CDPparticles had a mean diameter of roughly 50 nm.

A mixed suspension of about 40 nm acetylene black particles (Aldrich)and about 20 nm platinum particles (available from Alfa Aesar) wasprepared in approximately 100% pure ethanol (available fromPharmco-Aaper, grade ACS/USP). The mass concentrations of carbon andplatinum were about 0.5 mg/mL and 2.0 mg/mL, respectively. Thesuspension was atomized in a second atomizer at a rate of about 1mL/min. After about a 10 minute deposition onto a 1 inch diameter pieceof carbon filter, the resulting dark, fluffy, uniform film weighed about3.2 mg. Energy-dispersive X-ray analysis of the film yield acarbon/CDP/platinum mass ration of about 2/3/3.

The first and second atomizers used in the previous example were madefrom a drug delivery system for asthma, available from Southeast MedicalSupply, that were modified to increase the liquid reservoir volume andsupply gas pressure. The atomizers were modified by cutting and drillingholes into the body of the liquid reservoir and fitting tubing on theinlet and outlet of the reservoir. The entire assembly was subsequentlyplaced into a larger glass reservoir fitted with flow feedthroughs forthe inlet and outlet. The larger reservoir was filled with the solutionor suspension to be atomized, and the holes cut into the originalreservoir allowed the liquid to pass into the atomization region. Thesemodifications allowed for a larger volume of liquid to be atomized.

Using an apparatus as illustrated in FIG. 3, additional multicomponentparticle films were prepared. For example, solid acid CDP particles wereproduced by solution atomization of a CDP/water solution having aconcentration of about 0.5 mg/mL which was prepared by combining cesiumcarbonate (available from Alfa Aesar) and orthophosphoric acid(available from Alfa Aesar). The CDP water solution was atomized withthe custom atomizer described in the previous example. Platinum (Pt)nanoparticles having a diameter of about 20 nm were aerosolized byatomizing a suspension of Pt powder in ethanol using a Model 3076solution atomizer available from TSI, Inc. The aerosols from theatomization of CDP/water solution and platinum suspension was combinedand dried with heat from a lean premixed flame. The lean premixed flamewas formed by combusting a mixture of ethylene and air at an equivalenceratio of less than unity. The aerosolized components were mixed in thegas phase and then collected onto a carbon filter.

In a separate sample preparation, carbon nanoparticles were combinedwith the CDP and Pt aerosols prepared in the previous example. Thecarbon particles were formed with a Bunsen burner by making the Bunsenburner combust a fuel that was more rich in hydrocarbon by igniting ahydrocarbon rich mixture of ethylene, oxygen, and argon. The Bunsenburner thus produced carbon particles that were combined with CDP and Ptparticles from the two atomizers in the apparatus. The Bunsen burner inthis example thus served the dual purpose of drying the atomizeddroplets of the CDP solution and Pt suspension, and forming the carbonparticles.

Example parameters used in the formation of a multicomponent C/CDP/Ptfilm using an apparatus as illustrated in FIG. 3 are as follows. Anaqueous CDP solution having a concentration of 4 mg/mL was atomized inat a rate of 0.4 mL/min, forming CDP particles having a mean diameter ofroughly 200 nm. A suspension of about 20 nm platinum particles inethanol having a mass concentration of about 1.3 mg/mL was atomized inat a rate of about 0.2 mL/min. The flame was produced from a premixedflow of about 0.2 L/min of ethylene and about 1.4 L/min of air. After a1 hour deposition onto a 1 inch diameter piece of carbon filter, theresulting film was a well-mixed black, fluffy film that weighed about100 mg. The components weighed as follows: about 41 mg of carbon; about50 mg of CDP; and about 9 mg of platinum.

Using an apparatus as illustrated in FIG. 4, a multicomponentnanoparticle film of titania and carbon was prepared. In this example,titania particles having an average size of about 10 nm were produced instagnation flame 412 from burner 410 by injecting and vaporizingtitanium isopropoxide (available from Alfa-Aesar) into the combustibleethylene/oxygen/argon mixture by use of a syringe pump through a needle.Carbon particles 404 having an average agglomerate size of about 50 nmwere produced from burner 402 from a flame by combusting an ethylene/airmixture having an equivalence ratio of greater than 1.8. Themulticomponent nanoparticle film of titania and carbon was produced on aglass substrate fixed to rotating plate 406. As shown in the electronmicrograph image of FIG. 5, the multicomponent film is a well-mixed filmcomposed of titania and carbon nanoparticles.

FIG. 7 illustrates the distribution of a mixed aerosol containing carbonand CDP particles. The carbon particles were formed by a fuel-richpremixed ethylene/oxygen flame having an equivalence ratio of 2.0. TheCDP particles were formed by solution atomization, wherein a 0.5 mg/mLaqueous CDP solution was atomized, and the resulting aerosolizeddroplets mixed with the hot gas (about 250 degrees Celsius) containingthe carbon particles formed in the flame. The particle size distributionwas determined by a scanning mobility particle sizer (nano-SMPS analyzermodel 3936N25, available from TSI, Inc. As shows in the figure, theflame-generated carbon particles exhibit a large peak near about 10 nmand the CDP particles exhibit a smaller broader peak near about 50 nm.

Using an apparatus as illustrated in FIG. 8, a composite comprising aplurality of lithium iron phosphate particles and a plurality of carbonwas prepared. The composite was prepared by combining an aerosol oflithium iron phosphate nanoparticles with an aerosol of carbon particlesin a chamber having a reducing environment.

Initially, an acidic aqueous precursor solution was prepared bycombining about 3.69 g of Li₂CO₃ (available from Alfa Aesar) with 19.28g of FeCl₂(4H₂O) (available from Alfa Aesar) with 7 mL of H₃PO₄(available from Alfa Aesar) with 200 mL of distilled water. The pH ofthe solution was adjusted by adding 5 mL of HCl.

The precursor solution was atomized in the atomizer at a rate of about0.1 mL/min with a stream of nitrogen gas. The atomizer that was used inthis experiment was a TSI Model 3076 atomizer which provided aerosolizeddroplets of approximately 4 microns. Carbon particles were produced bycombusting a mixture comprising propane and air at a ratio of about 1:22by volume.

The aerosolized precursor solution was passed through the flame used toproduce the carbon particles causing a further reduction in the size ofthe of the aerosol and subsequently produced lithium iron phosphateparticles possibly due to microexplosion of the droplets as they enteredthe flame forming smaller satellite droplets, and drying of thesatellite droplets.

The dried lithium iron phosphate/carbon aerosol mixture was carriedthrough a conduit under temperatures exceeding 200 C due to the heatproduced by the flame. The heat combined with the carbon-rich andoxygen-deficient environment provides a reducing environment forminimizing the presence of Fe(III). The HCl acid added to the solutionremained in the gas phase and was carried out of the system with theflow.

The multicomponent aerosol itself may be collected by impaction,interception, diffusion, electrostatic precipitation, or thermophoresis.A simple way to collect the aerosol particles is to pass the flowthrough a carbon filter, which itself may serve as a lithium ion batterycathode. In this way, the lithium iron phosphate and carbon nanoparticleproduction, mixing, and collection onto a battery electrode isaccomplished in a single process.

Only the preferred embodiments of the present invention and examples ofits versatility are shown and described in the present disclosure. It isto be understood that the present invention is capable of use in variousother combinations and environments and is capable of changes ormodifications within the scope of the inventive concept as expressedherein. Thus, for example, those skilled in the art will recognize, orbe able to ascertain, using no more than routine experimentation,numerous equivalents to the specific substances, procedures andarrangements described herein. Such equivalents are considered to bewithin the scope of this invention, and are covered by the followingclaims.

1-15. (canceled)
 16. An apparatus for combining distinct aerosols, theapparatus comprising a first burner or atomizer for forming a firstaerosol; a second burner or atomizer forming a second aerosol; a chamberin fluid communication with the first and second burner or atomizer forreceiving and mixing the first and second aerosols; and an exit portconnected to the chamber for allowing the aerosols to escape thechamber, wherein the first burner or atomizer is capable of either: (a)forming an aerosol that is compositionally distinct from the aerosolformed from the second burner or atomizer or (b) forming an aerosol thathas an average size that is significantly different from the aerosolformed from the second burner or atomizer.
 17. The apparatus accordingto claim 16, wherein the apparatus comprises a first burner for formingthe first aerosol and a second atomizer forming the second aerosol. 18.The apparatus according to claim 16, wherein the first or second burneror atomizer has a nozzle or aperture in the form of a slot.
 19. Theapparatus according to claim 16, wherein the chamber or exit port isconfigured in the form of a slot.
 20. The apparatus according to claim16, wherein the first and second burner or atomizer and the chamber andexit port are configured in the form of a slot.
 21. A process of forminglithium active compound particles, the process comprising: forming anaerosol in a chamber from an aqueous medium of a lithium active compoundor a precursor thereof; and exposing the aerosol to a flame in thechamber which is substantially free of oxidants to form lithium activecompound particles.
 22. The process according to claim 21, wherein theaerosol is an aerosol of lithium iron phosphate or precursor thereof.23. The process according to claim 21, wherein the aqueous medium of thelithium active compound or precursor thereof is formed from any one oflithium acetate, lithium hydroxide, lithium nitrate, lithium oxalate,lithium oxide, lithium phosphate, lithium dihydrogen phosphate, lithiumcarbonate, iron sulfate, iron acetate, iron oxalate, iron citrate, oriron chloride.
 24. The process according to claim 21, further comprisingcollecting the lithium active compound particles as a film on asubstrate.
 25. The process according to claim 21, further comprisingforming a second aerosol of carbon particles in the chamber; andcombining the lithium active compound particles with the carbonparticles in the chamber to form a composite material.
 26. The processaccording to claim 25, wherein the carbon particles are formed byatomizing a suspension of carbon particles in a liquid medium.
 27. Theprocess according to claim 21, further comprising mixing carbon with thelithium active compound particles and depositing the mixture on asubstrate to form a cathode electrode.